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This module is intended to provide access to basic string functions.

Most of the functions provided here can be invoked with named parameters, unnamed parameters, or a mixture. If named parameters are used, Mediawiki will automatically remove any leading or trailing whitespace from the parameter. Depending on the intended use, it may be advantageous to either preserve or remove such whitespace.

Global options

ignore_errors
If set to true or 1, any error condition will result in an empty string being returned rather than an error message.
error_category
If an error occurs, specifies the name of a category to include with the error message. The default category is Errors reported by Module String.
no_category
If set to true or 1, no category will be added if an error is generated.

local str = {}

-- Cannot include null byte.
local UTF8_char = "[\1-\127\194-\244][\128-\191]*"

--[[
ulen

Counts UTF-8 characters. Faster than mw.ustring.len.

Assumes that the encoding is correct. Unlike mw.ustring.len, does not return nil
if encoding is invalid.

Does not count the bytes 192, 193, and 245-255. They are not used in UTF-8 and
will not occur if the string is valid. They are replaced with the replacement
character (U+FFFD) on MediaWiki pages.
--]]
function str.ulen(text)
	local _, length = string.gsub(text, UTF8_char, "")
	return length
end

--[[
len

This function returns the length of the target string.

Usage:
{{#invoke:string|len|target_string|}}
OR
{{#invoke:string|len|s=target_string}}

Parameters
    s: The string whose length to report

If invoked using named parameters, Mediawiki will automatically remove any leading or
trailing whitespace from the target string.
]]
function str.len(frame)
	local new_args = str._getParameters(frame.args, { 's' });
	local s = new_args['s'] or '';
	return mw.ustring.len(s)
end

--[[
sub

This function returns a substring of the target string at specified indices.

Usage:
{{#invoke:string|sub|target_string|start_index|end_index}}
OR
{{#invoke:string|sub|s=target_string|i=start_index|j=end_index}}

Parameters
    s: The string to return a subset of
    i: The fist index of the substring to return, defaults to 1.
    j: The last index of the string to return, defaults to the last character.
    
The first character of the string is assigned an index of 1.  If either i or j
is a negative value, it is interpreted the same as selecting a character by
counting from the end of the string.  Hence, a value of -1 is the same as
selecting the last character of the string.

If the requested indices are out of range for the given string, an error is
reported.
]]
function str.sub(frame)
	local new_args = str._getParameters(frame.args, { 's', 'i', 'j' });
	local s = new_args['s'] or '';
	local i = tonumber(new_args['i']) or 1;
	local j = tonumber(new_args['j']) or -1;
	
	local len = mw.ustring.len(s);
	
	-- Convert negatives for range checking
	if i < 0 then
		i = len + i + 1;
	end
	if j < 0 then
		j = len + j + 1;
	end
	
	if i > len or j > len or i < 1 or j < 1 then
		return str._error('String subset index out of range');
	end
	if j < i then
		return str._error('String subset indices out of order');
	end
	
	return mw.ustring.sub(s, i, j)
end

--[[
This function implements that features of {{str sub old}} and is kept in order
to maintain these older templates.
]]
function str.sublength(frame)
	local i = tonumber(frame.args.i) or 0
	local len = tonumber(frame.args.len)
	return mw.ustring.sub(frame.args.s, i + 1, len and (i + len))
end

--[[
match

This function returns a substring from the source string that matches a
specified pattern.

Usage:
{{#invoke:string|match|source_string|pattern_string|start_index|match_number|plain_flag|nomatch_output}}
OR
{{#invoke:string|pos|s=source_string|pattern=pattern_string|start=start_index
    |match=match_number|plain=plain_flag|nomatch=nomatch_output}}

Parameters
    s: The string to search
    pattern: The pattern or string to find within the string
    start: The index within the source string to start the search.  The first
        character of the string has index 1.  Defaults to 1.
    match: In some cases it may be possible to make multiple matches on a single
        string.  This specifies which match to return, where the first match is
        match= 1.  If a negative number is specified then a match is returned
        counting from the last match.  Hence match = -1 is the same as requesting
        the last match.  Defaults to 1.
    plain: A flag indicating that the pattern should be understood as plain
        text.  Defaults to false.
    nomatch: If no match is found, output the "nomatch" value rather than an error.

If invoked using named parameters, Mediawiki will automatically remove any leading or
trailing whitespace from each string.  In some circumstances this is desirable, in
other cases one may want to preserve the whitespace.

If the match_number or start_index are out of range for the string being queried, then
this function generates an error.  An error is also generated if no match is found.
If one adds the parameter ignore_errors=true, then the error will be suppressed and
an empty string will be returned on any failure.

For information on constructing Lua patterns, a form of [regular expression], see:

* http://www.lua.org/manual/5.1/manual.html#5.4.1
* http://www.mediawiki.org/wiki/Extension:Scribunto/Lua_reference_manual#Patterns
* http://www.mediawiki.org/wiki/Extension:Scribunto/Lua_reference_manual#Ustring_patterns

]]
function str.match(frame)
	local new_args = str._getParameters(frame.args, { 's', 'pattern', 'start', 'match', 'plain', 'nomatch' });
	local s = new_args['s'] or '';
	local start = tonumber(new_args['start']) or 1;
	local plain_flag = str._getBoolean(new_args['plain'] or false);
	local pattern = new_args['pattern'] or '';
	local match_index = math.floor(tonumber(new_args['match']) or 1);
	local nomatch = new_args['nomatch'];
	
	if s == '' then
		return str._error('Target string is empty');
	end
	if pattern == '' then
		return str._error('Pattern string is empty');
	end
	if math.abs(start) < 1 or math.abs(start) > mw.ustring.len(s) then
		return str._error('Requested start is out of range');
	end
	if match_index == 0 then
		return str._error('Match index is out of range');
	end
	if plain_flag then
		pattern = str.pattern_escape(pattern);
	end
	
	local result
	if match_index == 1 then
		-- Find first match is simple case
		result = mw.ustring.match(s, pattern, start)
	else
		if start > 1 then
			s = mw.ustring.sub(s, start);
		end
		
		local iterator = mw.ustring.gmatch(s, pattern);
		if match_index > 0 then
			-- Forward search
			for w in iterator do
				match_index = match_index - 1;
				if match_index == 0 then
					result = w;
					break;
				end
			end
		else
			-- Reverse search
			local result_table = {};
			local count = 1;
			for w in iterator do
				result_table[count] = w;
				count = count + 1;
			end
			
			result = result_table[count + match_index];
		end
	end
	
	if result == nil then
		if nomatch == nil then
			return str._error('Match not found');
		else
			return nomatch;
		end
	else
		return result;
	end
end

--[[
pos

This function returns a single character from the target string at position pos.

Usage:
{{#invoke:string|pos|target_string|index_value}}
OR
{{#invoke:string|pos|target=target_string|pos=index_value}}

Parameters
    target: The string to search
    pos: The index for the character to return

If invoked using named parameters, Mediawiki will automatically remove any leading or
trailing whitespace from the target string.  In some circumstances this is desirable, in
other cases one may want to preserve the whitespace.

The first character has an index value of 1.

If one requests a negative value, this function will select a character by counting backwards
from the end of the string.  In other words pos = -1 is the same as asking for the last character.

A requested value of zero, or a value greater than the length of the string returns an error.
]]
function str.pos(frame)
	local new_args = str._getParameters(frame.args, { 'target', 'pos' });
	local target_str = new_args['target'] or '';
	local pos = tonumber(new_args['pos']) or 0;
	
	if pos == 0 or math.abs(pos) > mw.ustring.len(target_str) then
		return str._error('String index out of range');
	end
	
	return mw.ustring.sub(target_str, pos, pos);
end

--[[
str_find

This function duplicates the behavior of {{str_find}}, including all of its quirks.
This is provided in order to support existing templates, but is NOT RECOMMENDED for
new code and templates.  New code is recommended to use the "find" function instead.

Returns the first index in "source" that is a match to "target".  Indexing is 1-based,
and the function returns -1 if the "target" string is not present in "source".

Important Note: If the "target" string is empty / missing, this function returns a
value of "1", which is generally unexpected behavior, and must be accounted for
separatetly.
]]
function str.str_find(frame)
	local new_args = str._getParameters(frame.args, { 'source', 'target' });
	local source_str = new_args['source'] or '';
	local target_str = new_args['target'] or '';
	
	if target_str == '' then
		return 1;
	end
	
	local start = mw.ustring.find(source_str, target_str, 1, true)
	if start == nil then
		start = -1
	end
	
	return start
end

--[[
find

This function allows one to search for a target string or pattern within another
string.

Usage:
{{#invoke:string|find|source_str|target_string|start_index|plain_flag}}
OR
{{#invoke:string|find|source=source_str|target=target_str|start=start_index|plain=plain_flag}}

Parameters
    source: The string to search
    target: The string or pattern to find within source
    start: The index within the source string to start the search, defaults to 1
    plain: Boolean flag indicating that target should be understood as plain
        text and not as a Lua style regular expression, defaults to true

If invoked using named parameters, Mediawiki will automatically remove any leading or
trailing whitespace from the parameter.  In some circumstances this is desirable, in
other cases one may want to preserve the whitespace.

This function returns the first index >= "start" where "target" can be found
within "source".  Indices are 1-based.  If "target" is not found, then this
function returns an empty string.  If either "source" or "target" are missing / empty, this
function also returns an empty string.

This function should be safe for UTF-8 strings.
]]
function str.find(frame)
	local params = {
		[1] = { required = true },
		[2] = { required = true },
		[3] = { type = "number" },
		[4] = { type = "boolean" },
	}
	
	local args = require("Module:parameters").process(frame.args, params)
	
	return mw.ustring.find(args[1], args[2], args[3], args[4])
end

--[[
replace

This function allows one to replace a target string or pattern within another
string.

Usage:
{{#invoke:string|replace|source_str|pattern_string|replace_string|replacement_count|plain_flag}}
OR
{{#invoke:string|replace|source=source_string|pattern=pattern_string|replace=replace_string|
   count=replacement_count|plain=plain_flag}}

Parameters
    source: The string to search
    pattern: The string or pattern to find within source
    replace: The replacement text
    count: The number of occurences to replace, defaults to all.
    plain: Boolean flag indicating that pattern should be understood as plain
        text and not as a Lua style regular expression, defaults to true
]]
function str.replace(frame)
	local new_args = str._getParameters(frame.args, { 'source', 'pattern', 'replace', 'count', 'plain' });
	local source_str = new_args['source'] or '';
	local pattern = new_args['pattern'] or '';
	local replace = new_args['replace'] or '';
	local count = tonumber(new_args['count']);
	local plain = new_args['plain'] or true;
	
	if source_str == '' or pattern == '' then
		return source_str;
	end
	plain = str._getBoolean(plain);
	
	if plain then
		pattern = str.pattern_escape(pattern);
		replace = mw.ustring.gsub(replace, "%%", "%%%%"); --Only need to escape replacement sequences.
	end
	
	local result;
	
	if count ~= nil then
		result = mw.ustring.gsub(source_str, pattern, replace, count);
	else
		result = mw.ustring.gsub(source_str, pattern, replace);
	end
	
	return result;
end


function str.gsub(frame)
	local params = {
		[1] = { required = true, allow_empty = true },
		[2] = { required = true, allow_empty = true },
		[3] = { required = true, allow_empty = true },
		[4] = { type = "number" },
	}
	
	local args = require("Module:parameters").process(frame.args, params)
	
	return (mw.ustring.gsub(args[1], args[2], args[3], args[4]))
end


--[[
    simple function to pipe string.rep to templates.
]]

function str.rep(frame)
	local repetitions = tonumber(frame.args[2])
	if not repetitions then
		return str._error('function rep expects a number as second parameter, received "' .. (frame.args[2] or '') .. '"')
	end
	return string.rep(frame.args[1] or '', repetitions)
end

function str.lower(frame)
	local text = frame.args[1] or ''
	return mw.ustring.lower(text)
end

str.lc = str.lower

--[[
Helper function that populates the argument list given that user may need to use a mix of
named and unnamed parameters.  This is relevant because named parameters are not
identical to unnamed parameters due to string trimming, and when dealing with strings
we sometimes want to either preserve or remove that whitespace depending on the application.
]]
function str._getParameters(frame_args, arg_list)
	local new_args = {};
	local index = 1;
	local value;
	
	for _, arg in ipairs(arg_list) do
		value = frame_args[arg]
		if value == nil then
			value = frame_args[index];
			index = index + 1;
		end
		new_args[arg] = value;
	end
	
	return new_args;
end

--[[
Helper function to handle error messages.
]]
function str._error(error_str)
	local frame = mw.getCurrentFrame();
	local error_category = frame.args.error_category or 'Errors reported by Module String';
	local ignore_errors = frame.args.ignore_errors or false;
	local no_category = frame.args.no_category or false;
	
	if str._getBoolean(ignore_errors) then
		return '';
	end
	
	local error_str = '<strong class="error">String Module Error: ' .. error_str .. '</strong>';
	if error_category ~= '' and not str._getBoolean(no_category) then
		error_str = '[[Category:' .. error_category .. ']]' .. error_str;
	end
	
	return error_str;
end

--[[
Helper Function to interpret boolean strings
]]
function str._getBoolean(boolean_str)
	local boolean_value;
	
	if type(boolean_str) == 'string' then
		boolean_str = boolean_str:lower();
		if boolean_str == 'false' or boolean_str == 'no' or boolean_str == '0'
				or boolean_str == '' then
			boolean_value = false;
		else
			boolean_value = true;
		end
	elseif type(boolean_str) == 'boolean' then
		boolean_value = boolean_str;
	else
		error('No boolean value found');
	end
	return boolean_value
end

--[[
Helper function that escapes all pattern characters – ().%+-*?[^$] – so that they will be treated
as plain text.
]]
function str.pattern_escape(pattern_str)
	local invoked = false
	
	if type(pattern_str) == "table" then
		if pattern_str.args then
			local frame = pattern_str
			invoked = true
			
			if frame.args[1] then
				pattern_str = frame.args[1]
			else
				pattern_str = frame:getParent().args[1]
			end
		else
			error("First argument to pattern_escape should be a string, a number, or a frame object.")
		end
	elseif not (type(pattern_str) == "string" or type(pattern_str) == "number") then
		error("First argument to pattern_escape should be a string or a number.")
	end
	
	if invoked then
		local escaped = mw.ustring.gsub(pattern_str, "([%(%)%.%%%+%-%*%?%[%^%$%]])", "%%%1")
		return escaped
	else
		return mw.ustring.gsub(pattern_str, "([%(%)%.%%%+%-%*%?%[%^%$%]])", "%%%1");
	end
end

function str.count(text, pattern, plain)
	if not (type(text) == "string" or type(text) == "number") then
		error('The first argument to the function "count" must be a string or a number, not a ' .. type(text) .. '.')
	end
	
	if not (type(pattern) == "string" or type(pattern) == "number") then
		error('The first argument to the function "count" must be a string or a number, not a ' .. type(text) .. '.')
	end
	
	if plain then
		pattern = str.pattern_escape(pattern)
	end
	
	local _, count = mw.ustring.gsub(text, pattern, "")
	
	return count
end

function str.plain_gsub(text, pattern, replacement)
	local invoked = false
	
	if type(text) == "table" then
		invoked = true
		
		if text.args then
			local frame = text
			
			local params = {
				[1] = {},
				[2] = {},
				[3] = { allow_empty = true },
			}
			
			local args = require("Module:parameters").process(frame.args, params)
			
			text = args[1]
			pattern = args[2]
			replacement = args[3]
		else
			error("If the first argument to plain_gsub is a table, it should be a frame object.")
		end
	else
		if not (type(pattern) == "string" or type(pattern) == "number") then
			error("The second argument to plain_gsub should be a string or a number.")
		end
		
		if not (type(replacement) == "string" or type(replacement) == "number") then
			error("The third argument to plain_gsub should be a string or a number.")
		end
	end
	
	pattern = str.pattern_escape(pattern)
	
	if invoked then
		text = mw.ustring.gsub(text, pattern, replacement)
		return text
	else
		return mw.ustring.gsub(text, pattern, replacement)
	end
end

function str.matchToArray(text, pattern)
	local invoked = false
	
	if type(text) == "table" then
		invoked = true
		
		if text.args then
			local frame = text
			
			local params = {
				[1] = { required = true },
				[2] = { required = true },
			}
			
			local args = require("Module:parameters").process(frame.args, params)
			
			text = args[1]
			pattern = args[2]
		else
			error("If the first argument to plain_gsub is a table, it should be a frame object.")
		end
	else
		if not (type(pattern) == "string" or type(pattern) == "number") then
			error("The second argument to plain_gsub should be a string or a number.")
		end
	end
	
	local matches = {}
	local i = 0
	for match in mw.ustring.gmatch(text, pattern) do
		i = i + 1
		matches[i] = match
	end
	
	if i > 0 then
		if invoked then
			return table.concat(matches, ", ")
		else
			return matches
		end
	else
		if invoked then
			return ""
		else
			return nil
		end
	end
end

--[=[
	Similar to gmatch, but it returns the count of the match in addition to the
	list of captures, something like ipairs().
	
	If the pattern doesn't contain any captures, the whole match is returned.
	
	Invoke thus:
	
		for i, whole_match in require("Module:string").imatch(text, pattern) do
			[ do something with i and whole_match ]
		end
	
	or
	
		for i, capture1[, capture2[, capture3[, ...]]] in require("Module:string").imatch(text, pattern) do
			[ do something with i and capture1 ]
		end
	
	For example, this code
		for i, whole_match in require("Module:string").imatch("a b"c", "[a-z]") do
			mw.log(i, whole_match)
		end
	will log
		1	a
		2	b
		3	c
]=]
function str.imatch(text, pattern, pos, plain, use_basic_Lua_function)
	local i = 0
	pos = pos or 0
	if not string.find(pattern, "%b()") then
		pattern = "(" .. pattern .. ")"
	end
	local find = use_basic_Lua_function and string.find or mw.ustring.find
	return function()
		i = i + 1
		local return_values = { find(text, pattern, pos, plain) }
		local j = return_values[2]
		
		if return_values[3] then
			pos = j + 1
			-- Skip the first two returned values, which are the indices of the
			-- whole match.
			return i, unpack(return_values, 3)
		end
	end
end

function str.escapebytes(s)
	return (string.gsub(s,
		'.',
		function(char)
			return ('\\%03d'):format(string.byte(char))
		end))
end

return str